Wrench Capability Analysis of Aerial Cable Towed Systems

International audienceAerial cable towed systems (ACTSs) can be created by joining unmanned aerial vehicles (UAVs) to a payload to extend the capabilities of the system beyond those of an individual UAV. This paper describes a systematic method of evaluating the avail- able wrench set and the robustness of equilibrium of ACTSs by adapting wrench analysis techniques used in cable-driven parallel robots to account for the constraints of quadrotor actuation. Case studies are provided to demonstrate the analysis of different classes of ACTSs, as a means of evaluating the design and operating configurations

Increasing energy efficiency of high-speed parallel robots by using variable stiffness springs and optimal motion generation

International audienceThe classical approach to decrease the energy consumption of high-speed robots is by lowering the moving elements mass in order to have a lightweight structure. Even if this allows reducing the energy consumed, the lightweight architecture affects the robot stiffness, worsening the accuracy of the mechanism. Recently, variable stiffness actuators (VSAs) have been used in order to reduce the energy consumption of high-speed pick-and-place robots. The idea is to smartly tune online the stiffness of VSA springs so that the robot is put in near a resonance mode, thus considerably decreasing the energy consumption during fast pseudo-periodic pick-and-place motions. However, the serial configuration of springs and motors in the VSA leads to uncontrolled robot deflections at high-speeds and, thus, to a poor positioning accuracy of its end-effector. In order to avoid these drawbacks and to increase the energy efficiency while ensuring the accuracy, this paper proposes the use of parallel arrangement of variable stiffness springs (VSS) and motors, combined with an energy-based optimal trajectory planner. The VSS are used as energy storage for carrying out the reduction of the energy consumption and their parallel configuration with the motors ensure the load balancing at high-speed without losing the accuracy of the robot. Simulations of the suggested approach on a five-bar mechanism are performed and show the increase on energy efficiency. 1 INTRODUCTION It is well-known that in industrial applications, such as high-speed pick-and-place operations, parallel robots are widely used [1, 2]. Repeatability and accuracy are typically the most important criteria to measure their performance. Nevertheless, the design trends to operate at high speeds are shifting to the design of robots with lightweight architectures [3] in order to decrease the energy consumed by the motors, and measure as well the robot performance based on its energy efficiency [4]. For slow motions, gravity-balancing techniques [5-8] have been proposed in order to compensate the input efforts required to move the links of a pick-and-place robot, and thus to avoid consuming energy. Even if these methods have shown their effectiveness at slow speeds, it is not the case for high-speed operations in which the inertial effects are preponderant. A first solution introduced the series elastic actuators (SEAs) [9] to cope with the energy storage issues. The SEAs are compliant actua-tors composed by a motor which is linked to a spring in series that serves as energy storage, and whose stiffness is set by the spring constant. SEAs were first used to absorb contact shocks and to reduce the peak forces due to the impacts in bipedal walking robots [10]. The limitation of the SEAs is that the stiffness is fixed and cannot be altered during motion, thus limiting the level of compliance to adapt for different tasks. Therefore, a recent second solution proposed the use of variable stiffness actuators (VSAs) [11-13] to handle with energy storage issues. VSAs co

Predictive scheme for observer-based control of LTI systems with unknown disturbances

International audienceIn this work, it is shown that the results introduced in [1], that hold for full state measurement, can be extended to partial state measurement. In particular, it is proven that the combination of an observer with the new predictive scheme of [1] leads to a better disturbance attenuation than using the same observer with the standard predictive scheme. Finally, some simulations illustrate the results for constant and time-varying disturbances

New predictive scheme for the control of LTI systems with input delay and unknown disturbances

International audienceA new predictive scheme is proposed for the control of Linear Time Invariant (LTI) systems with a constant and known delay in the input and unknown disturbances. It has been achieved to include disturbances effect in the prediction even though there are completely unknown. The Artstein reduction is thenrevisited thanks to the computation of this new prediction. An extensive comparison with the standard scheme is presented throughout the article. It is proved that the new scheme leads to feedback controllers that are able to reject perfectly constant disturbances. For time-varying ones, a better attenuation is achieved for a wide range of perturbations and for both linear and nonlinear controllers. A criterion is given to characterize this class of perturbations. Finally, some simulations illustrate the results

Minimizing the Energy Consumption of a Delta Robot by Exploiting the Natural Dynamics

International audienceIt is known that when performing high-speed pick-and-place motions in robot manipulators, an enormous amount of energy is dissipated in order to stop the robot during the braking phase. Typically, this energy is lost as heat in the braking resistances of the motor drivers, leading to increase the energetic losses in the actuation chain. In order to improve the energy efficiency while ensuring accuracy at high-speeds, this paper proposes the use of variable stiffness springs (VSS) in parallel configuration with the motors. This actuation chain is combined with a motion generator which seeks to exploit the robot natural dynamics by adjusting the equilibrium position of the VSS so that the robot is put in near resonance, thus decreasing the energetic losses. Simulations of the suggested approach on a Delta robot are performed and show the drastic reduction of energy consumption

Minimizing the Energy Consumption of a Delta Robot by Exploiting the Natural Dynamics

International audienceIt is known that when performing high-speed pick-and-place motions in robot manipulators, an enormous amount of energy is dissipated in order to stop the robot during the braking phase. Typically, this energy is lost as heat in the braking resistances of the motor drivers, leading to increase the energetic losses in the actuation chain. In order to improve the energy efficiency while ensuring accuracy at high-speeds, this paper proposes the use of variable stiffness springs (VSS) in parallel configuration with the motors. This actuation chain is combined with a motion generator which seeks to exploit the robot natural dynamics by adjusting the equilibrium position of the VSS so that the robot is put in near resonance, thus decreasing the energetic losses. Simulations of the suggested approach on a Delta robot are performed and show the drastic reduction of energy consumption

VENTANAS DEL NUBLO [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201

Decentralized control and state estimation of a flying parallel robot interacting with the environment

International audienceUnmanned Aerial Vehicles (UAVs) have great potential to achieve a variety of tasks remotely such as aerial grasping, transporting and manipulating objects. Architectures with multiple UAVs have further enhanced the payload capacity and manipulability of these robots, for instance a Flying Parallel Robot (FPR) where a moving platform is cooperatively supported by multiple quadrotors with passive rigid links. In this paper, we address the vision-based state estimation and decentralized control applied to the multi-UAV parallel robot, taking the FPR as an example. An ArUco marker system is applied to estimate the relative pose of each UAV with respect to the common platform frame, along with the Extended Kalman Filter to reconstruct the robot state without the dependence on any external localization system. The interaction controller is then deployed in a decentralized manner, which is potentially more robust to communication delays or interruptions. The proposed methodology has been validated by real-time experiments demonstrating the teleoperation of the FPR interacting with the environment

Control and Configuration Planning of an Aerial Cable Towed System

International audienceThis paper investigates the effect of the robot configuration on the performance of an aerial cable towed system (ACTS) composed of three quadrotors manipulating a point mass payload. The kinematic and dynamic models of the ACTS are derived in a minimal set of geometric coordinates, and a centralized feedback linearization controller is developed. Independent to the payload trajectory, the configuration of the ACTS is controlled and is evaluated using a robustness index named the capacity margin. Experimental validation is performed with optimal, suboptimal, and wrench infeasible configurations. It is shown that configurations near the point of zero capacity margin allow the ACTS to hover but not to follow dynamic trajectories, and that the ACTS cannot fly with a negative capacity margin. Dynamic tests are performed on the ACTS, showing the effects of the configuration on the achievable accelerations